1. Field of the Invention
The present invention relates to the detection of a rotation angle of a conveying roller in a recording apparatus.
2. Related Background Art
Generally speaking, recording apparatuses, such as printers, copying machines, and facsimile apparatuses, record an image consisting of a dot pattern on a recording sheet, such as a paper sheet or a thin plastic plate, by driving an energy generator of a recording head in accordance with image information.
Such recording apparatuses can be classified, in terms of recording system, into ink-jet type apparatuses, wire-dot type apparatuses, thermal type apparatuses, laser-beam type apparatuses, etc. Of these, in the ink-jet type recording apparatuses, recording is effected by discharging droplets of ink (recording liquid) from discharge holes of a recording head and causing them to adhere to a recording sheet.
Further, in terms of recording mechanism construction, such apparatuses can be classified into full-line type and serial type apparatuses. A full-line type apparatus has a recording means comprising recording elements arranged over the entire recording width range extending perpendicular to the recording sheet conveying direction, recording being performed by moving the recording sheet in the sub scanning direction (the recording sheet conveying direction). In a serial type apparatus, recording is effected by performing scanning with a recording means mounted on a carriage movable in the main scanning direction and moving the recording sheet in the sub scanning direction. In particular, the serial type apparatus, which needs no such wide recording means as used in the full-line type apparatus, is relatively inexpensive and is now in widespread use.
Conventionally, an open loop control system using a stepping motor has been mainly adopted in the means for moving the recording sheet in the sub scanning direction, i.e., the so-called sheet conveying means. Recently, however, there is an increasing demand for high image quality, and it is rather difficult to meet this demand with the open loop control system. In view of this, adoption of a feedback control system is required in which, to effect high-quality conveyance control, the rotation angle of the conveying roller when conveying the recording sheet is detected to control the rotation of the conveying roller, etc.
However, while it is desirable that an encoder wheel on which a scale is written (formed) in advance be mounted to the conveying roller such that their centers of rotation (axes) coincide with each other, generation of offset between the center of rotation of the conveyance outer peripheral portion of the conveying roller and the center of rotation of the detecting portion of the encoder wheel cannot be avoided because of the play between the mounting holes and the encoder wheel, etc.